Mobile devices such as smart phones are rapidly evolving and maturing as a platform to serve the computational and communication needs of users. A growing number of mobile phones have embedded sensors which can sense aspects of a user's environment. For example, many smart phones include built-in accelerometers, global positioning system (GPS) functionality, light sensors, microphones, proximity sensors, cameras, compasses, and gyroscopes. Additionally, there are sensors available that can communicate using low power RF communication technology and push data to mobile devices. These sensors, along with the local computational power and the communication capability built into the mobile devices, enable applications in fields such as location-based tracking, healthcare, remote monitoring, and environmental monitoring.